_C_ License Applicability. Except to the extent portions of this file are
_C_ made subject to an alternative license as permitted in the SGI Free
_C_ Software License B, Version 1.1 (the "License"), the contents of this
_C_ file are subject only to the provisions of the License. You may not use
_C_ this file except in compliance with the License. You may obtain a copy
_C_ of the License at Silicon Graphics, Inc., attn: Legal Services, 1600
_C_ Amphitheatre Parkway, Mountain View, CA 94043-1351, or at:
_C_ 
_C_ http://oss.sgi.com/projects/FreeB
_C_ 
_C_ Note that, as provided in the License, the Software is distributed on an
_C_ "AS IS" basis, with ALL EXPRESS AND IMPLIED WARRANTIES AND CONDITIONS
_C_ DISCLAIMED, INCLUDING, WITHOUT LIMITATION, ANY IMPLIED WARRANTIES AND
_C_ CONDITIONS OF MERCHANTABILITY, SATISFACTORY QUALITY, FITNESS FOR A
_C_ PARTICULAR PURPOSE, AND NON-INFRINGEMENT.
_C_ 
_C_ Original Code. The Original Code is: OpenGL Sample Implementation,
_C_ Version 1.2.1, released January 26, 2000, developed by Silicon Graphics,
_C_ Inc. The Original Code is Copyright (c) 1991-2000 Silicon Graphics, Inc.
_C_ Copyright in any portions created by third parties is as indicated
_C_ elsewhere herein. All Rights Reserved.
_C_ 
_C_ Additional Notice Provisions: The application programming interfaces
_C_ established by SGI in conjunction with the Original Code are The
_C_ OpenGL(R) Graphics System: A Specification (Version 1.2.1), released
_C_ April 1, 1999; The OpenGL(R) Graphics System Utility Library (Version
_C_ 1.3), released November 4, 1998; and OpenGL(R) Graphics with the X
_C_ Window System(R) (Version 1.3), released October 19, 1998. This software
_C_ was created using the OpenGL(R) version 1.2.1 Sample Implementation
_C_ published by SGI, but has not been independently verified as being
_C_ compliant with the OpenGL(R) version 1.2.1 Specification.
_C_
_C_ The first character in this file must be an '_'!
_C_ Anything on a line after _C_ is ignored
_define(_filters,eqn)_C_
_C_    eqn is automatically replaced with neqn for nroff
_header(SelectBuffer,establish a buffer for selection mode values)
_names(SelectBuffer)
.SH PARAMETERS
_phead(_param1)
Specifies the size of _param2.
_phead(_param2)
Returns the selection data.
.SH DESCRIPTION
_cmnd has two arguments:
_param2 is a pointer to an array of unsigned integers,
and _param1 indicates the size of the array.
_param2 returns values from the name stack
(see _cmnd(InitNames), _cmnd(LoadName), _cmnd(PushName))
when the rendering mode is _const(SELECT) (see _cmnd(RenderMode)).
_cmnd must be issued before selection mode is enabled,
and it must not be issued while the rendering mode is _const(SELECT).
.P
A programmer can use selection to determine which primitives
are drawn into some region of a window.
The region is defined by the current modelview and perspective matrices. 
.P
In selection mode, no pixel fragments are produced from rasterization.
Instead,
if a primitive or a raster position intersects the clipping 
volume defined by the viewing frustum
and the user-defined clipping planes,
this primitive causes a selection hit.
(With polygons, no hit occurs if the polygon is culled.)
When a change is made to the name stack,
or when _cmnd(RenderMode) is called,
a hit record is copied to _param2 if any hits have occurred since the
last such event
(name stack change or 
_cmnd(RenderMode) call).
The hit record consists of the number of names in the name stack at the
time of the event, followed by the minimum and maximum depth values
of all vertices that hit since the previous event,
followed by the name stack contents,
bottom name first.
.P
Depth values (which are in the range [0,1]) are multiplied by 2^32 - 1,
before being placed in the hit record.
.P
An internal index into _param2 is reset to 0 whenever selection mode
is entered.
Each time a hit record is copied into _param2,
the index is incremented to point to the cell just past the end
of the block of names \- that is, to the next available cell.
If the hit record is larger than the number of remaining locations in _param2,
as much data as can fit is copied,
and the overflow flag is set.
If the name stack is empty when a hit record is copied,
that record consists of 0 followed by the minimum and maximum depth values.
.P
To exit selection mode, call _cmnd(RenderMode) with an argument
other than _const(SELECT).
Whenever _cmnd(RenderMode) is called while the render mode is _const(SELECT),
it returns the number of hit records copied to _param2,
resets the overflow flag and the selection buffer pointer,
and initializes the name stack to be empty.
If the overflow bit was set when _cmnd(RenderMode) was called,
a negative hit record count is returned.
.SH NOTES
The contents of _param2 is undefined until _cmnd(RenderMode) is called
with an argument other than _const(SELECT).
.P
_cmnd(Begin)/_cmnd(End) primitives and calls to _cmnd(RasterPos)
can result in hits.
.SH ERRORS
_const(INVALID_VALUE) is generated if _param1 is negative.
.P
_const(INVALID_OPERATION) is generated if _cmnd is called while the
render mode is _const(SELECT),
or if _cmnd(RenderMode) is called with argument _const(SELECT) before
_cmnd is called at least once.
.P
_const(INVALID_OPERATION) is generated if _cmnd
is executed between the execution of _cmnd(Begin)
and the corresponding execution of _cmnd(End).
.SH ASSOCIATED GETS
_cmnd(Get) with argument _const(NAME_STACK_DEPTH)
.br
_cmnd(Get) with argument _const(SELECTION_BUFFER_SIZE)
.br
_cmnd(GetPointerv) with argument _const(SELECTION_BUFFER_POINTER)
.SH SEE ALSO
_cmnd(FeedbackBuffer),
_cmnd(InitNames),
_cmnd(LoadName),
_cmnd(PushName),
_cmnd(RenderMode)